This invention relates to combination locks, and more particularly to a wheel pack and fence used in a conventional combination lock to render the combination lock radiographically secure.
Locks of the type commonly referred to as combination locks are of course well known. Generally such locks depend for their operation upon the alignment of a plurality of elements in a preselected manner which permits the operation of a bolt. These elements are usually in the form of discs commonly called wheels or tumblers, each of which is provided with a notch or recess called a gate. Such locks are generally provided with a wheel pack containing three such wheels each having a gate. However, more than three wheels can be provided. The gate of each of the wheels utilized must be properly aligned before the bolt can be moved. The security of such prior art locks depends mainly upon the fact that number of orders or permutations of the possible relative positions of each wheel before all gates are brought into registry is so large that the chance of these gates being aligned by a person not familiar with the combination is very small. However, relatively modern technology has made it possible to determine the combination to such prior art combination locks.
X-ray photography techniques will provide a flat photograph of the wheel pack that shows the position of the gate on each wheel. With this information one skilled in the art can readily operate the lock. In addition to X-ray techniques neutron beam gauging techniques will also reveal the combination. In such gauging techniques, a columnated neutron beam from, for example, a gamma neutron source, is aimed at the edge of the wheel pack and the location of a gate is indicated on a counting device by a higher count for a set time period. This higher count results from less metal or nylon being in the beam path when the beam passes through a gate.
Prior art combination locks that resist attack by the foregoing mentioned techniques have, of course, been developed. Some of these prior art locks use additional false wheels or tumblers, still others use gate shields and others use a plurality of gates only one of which is a true gate. Most of these prior art locks do provide a combination lock that resists attack by X-ray photography; however, some of these prior art locks are vulnerable to neutron gauging attack. Further, with many of these prior art locks a highly skilled person can utilize X-ray photography or neutron gauging to determine the combination. This task is exceedingly difficult to accomplish with some of the prior art locks but can be accomplished.
This invention provides a wheel-pack and fence for a conventional combination lock that converts the lock to a radiographically secure lock. With the wheel pack of this invention it is virtually impossible to determine the combination of the lock by X-ray photography technique or by neutron gauging techniques. Each wheel of the wheel pack of this invention contains a plurality of gates only one of which is a true gate. While this basic technique has been utilized in some prior art locks, the true-false gates of each wheel of the wheel pack of this invention are so formed and shaped that this invention provides an improvement over the prior art true-false gate devices.